Asexual propagation of plants has been shown for some species to yield large numbers of genetically identical embryos, each having a capacity to develop into a normal plant. Such embryos are usually further cultured under laboratory conditions until they reach an autotrophic “seedling” state characterized by an ability to produce its own food via photosynthesis, resist desiccation, produce roots able to penetrate soil, and fend off soil microorganisms. Some researchers have experimented with the production of artificial seeds, known as manufactured seeds, in which individual plant somatic or zygotic embryos are encapsulated in a seed coat. Examples of such manufactured seeds are disclosed in U.S. Pat. No. 5,701,699, issued to Carlson et al., the disclosure of which is hereby expressly incorporated by reference.
Typical manufactured seeds include a seed shell, synthetic gametophyte and a plant embryo. A manufactured seed that does not include the plant embryo is known in the art as a “seed blank.” The seed blank typically is a cylindrical capsule having a closed end and an open end. The synthetic gametophyte is placed within the seed shell to substantially fill the interior of the seed shell. A longitudinally extending hard porous insert, known as a cotyledon restraint, may be centrally located within one end of the seed shell, surrounded by the synthetic gametophyte, and includes a centrally located cavity extending partially through the length of the cotyledon restraint.
The cavity is sized to receive the plant embryo therein. The well-known plant embryo includes a radicle end and a cotyledon end. The plant embryo is deposited within the cavity of the cotyledon restraint, cotyledon end first. The plant embryo is then sealed within the seed blank by an end seat. There is a weakened spot in the end seal to allow the radicle end of the plant embryo to penetrate the end seal.
At has been discovered by the inventors of the present method that the rate of normal germination of an embryo from such manufactured seeds was unacceptably low. Their analysis noted that only about 30% of embryos within a study group of manufactured seeds produced a normal seedling having an expected root, cotyledons, etc. The present inventors observed that embryos, when inserted into the cavity of the cotyledon restraint having a diameter larger than the diameter of the embryo itself causes the cotyledons to be reflexed during somatic embryo development. This results in only the tips of the cotyledons to contact the walls of the cotyledon restraint cavity through which nutrition is passed from the gametophyte to the embryo. The present inventors theorize that this caused the unacceptably low productivity of the manufactured seeds.
Thus, there is a need for a method of preparing a material for use in a manufactured seed that improves the productivity of the manufactured seed.